Actron GM Code Scanner CP9001 - Manual (Page 28)

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can understand.
You can think of sensors as “high tech”
senders the devices found in older
vehicles for gauges and dashboard
message lights (oil pressure, fuel level,
etc.) Signals running into the computer
are referred to as “inputs.”
Sensors monitor such things as:
• Engine temperature
• Intake manifold vacuum
• Throttle position
• RPM
• Incoming air (temperature, amount)
• Exhaust gas oxygen content
Most engine computer systems will use
the sensor types listed above.
Additional sensors may be used
depending upon the engine, vehicle
type or other tasks the computer must
do. Note that information from one
sensor may be used by the computer
for many different tasks. For example,
engine temperature is something the
computer needs to know when
controlling fuel delivery, spark timing,
idle speed and emission systems. The
sensor information may be very
important for one engine control
function, but only used to “fine tune” a
second one.
There are several types of sensors
• Thermistor – This is a resistor
whose resistance changes with
temperature. It is used to measure
temperatures of coolant or incoming
air. It has two wires connected to it.
• Potentiometer – This signals a
position, such as throttle position or
EGR valve position. It connects to
three wires: one for power, one for
ground and one to carry the position
signal back to the computer.
• Switches – These are either ON
OUTPUT
AC
TUA
TORS
SENSORS
INPUT
BRAINS OF THE
COMPUTER
(voltage signal to the computer) or
OFF (no voltage signal to the
computer). Switches connect to two
wires and tell the computer simple
things, such as whether or not the
air conditioner is running.
• Signal Generator – These create
their own signal to tell the computer
of some condition, such as exhaust
gas oxygen content, camshaft
position, or intake manifold vacuum.
They may have one, two or three
wires connected to them.
The computer controls things with
actuators
The computer can only send out
electrical signals (referred to as
“outputs”). Devices called actuators
are powered by the computer to
control things. Actuator types include:
• Solenoids – These are used to
control a vacuum signal, bleed air,
control fuel flow, etc.
• Relays – These switch high
amperage power devices on and off,
such as electric fuel pumps or
electric cooling fans.
• Motors – Small motors are often
used to control idle speed.
Other output signals
Not all of the computer outgoing
signals go to actuators. Sometimes
information is sent to electronic
modules, such as ignition or trip
computer.
How the computer controls fuel
delivery
Good performance and low emissions
depend upon precise fuel control.
Early computer controlled vehicles
used electronically adjustable
carburetors, but fuel injectors were
soon introduced.
The job of the computer is to provide
the optimum mixture of air and fuel
(air/fuel ratio) to the engine for best
performance under all operating
conditions.